I think the subjectivity of charity oriented to a particular goal (say, saving lives) is hugely overrated. There's a substantial, thorough body of academic research around many interventions in global health development, and there's a lot of serious scientific work that's been done to determine what the consequences of funding particular interventions will be. While all science is subject to uncertainties and potential for revision, if you're willing to listen to your doctor when they say a particular medical procedure has been shown to reduce mortality from a condition you have, then you should be willing to listen to a development economist who says:
"From these trials, we concluded that ITNs reduce the child mortality from all causes, corresponding to a saving of 5.6 lives each year for every 1000 children protected with ITNs (high-certainty evidence)." Cochrane Collaboration systematic review
Knowing that, and knowing about organizations that distribute ITNs, what their budget is, and how many nets they distribute, you can figure out a best guess of how much it costs to save a life in this way. There's nothing subjective about it, it's all based on evidence, observations, and predictions.
Some existing work:
- GiveWell does a lot of analyzing this kind of research, and produces reports on their assessment of the evidence base for global health interventions. On the best interventions, it finds charities working on those programs and does in-depth analyses of their work, and how much further it would go with additional funding. Their aim is to make recommendations suitable for individual donors like yourself.
- The Open Philanthropy Project does more speculative and wide-ranging analyses with the aim of making giving recommendations to Good Ventures, a large philanthropic fund. They don't focus on recommendations for individual donors but they do publish a lot of their research and analysis in detail, which can give you insights into how full-time researchers might think about choosing between funding opportunities.
When you study evidence like this, one of the key lessons you learn is that which problem you are working on can be a much greater determinant in how much you achieve than how well you do it, how low your overheads are, or anything like that. Costs per life saved can span from mere thousands of US dollars to hundreds of thousands depending on how you try to do it, whereas it's really very unlikely that administrative costs and executive salaries will make a 100x difference in effectiveness (it would require comparing an organization wasting 99% of its budget with one wasting 0%!)
So, pick your focus area with particular attention to the evidence and reasoning around what effects it has, and find organizations working on it ideally with a strong track record and transparency in their operations.
It's worth remarking that in global health, there's a huge academic evidence base, lots of randomized controlled trials and systematic reviews, and generally you can hope for high-quality evidence. But there may be other areas that are just as important, where evidence is difficult or impossible to gather, e.g. around large-scale political reform, basic scientific research, or work to avoid rare but catastrophic events like pandemics or nuclear war. My advice there is to still consider the best arguments and evidence and academic work available, to work more from heuristics, historical analogies, and conceptual arguments -- but keep in mind always that there is still a fact of the matter about what the consequences of your actions will be, and what that is can vary dramatically depending on what you choose, so the importance of the problem you choose to work on still demands careful thought and analysis, because it will be the biggest factor on how much better off the world is with your contributions.
- It's not enough to find an important problem, if you don't have a strong reason to believe there is a tractable, feasible solution to it.
- It's not enough for an important problem to have a tractable solution, if the solution is not bottlenecked on funding. In that case your donation might not make more of the solution happen! (I've heard stories about organizations that partner with local doctors in the developing world to provide corrective surgeries, but run out of doctors before they run out of money, so they start paying doctors in other parts of the world to come and perform the surgeries, which is still valuable but much more expensive).
- Conversely, an intervention is more promising if there's some reason other people might have missed it. So for example, not everyone feels strongly about animal welfare, so if you do, you are likely to find better opportunities there; even among the money spent on animal welfare, a minority of it is spent on farmed animals, despite there being vastly more of them than pets or sanctuary animals, so if you care about those two groups equally, one represents more potential opportunities to help.